Objective: Define the role of the blood-brain barrier (BBB) in regulating the environment of the normal and neoplastic brain. Approach: Using the indicator diffusion and brain uptake methods, a map of the regional capacity of the BBB to transport certain carbohydrate and amino acid substrates is being accomplished. The effect of ischemia, hypoxia, various forms of radiation, and induced CNS neoplasia on the biochemical and morphological substrate of the BBB and will be studied.